Impulse recording optical system



\SS REFERENQE 1950 J. A. MAURER, JR

IMPULSE RECORDING OPTICAL SYSTEM 2 Sheets-Sheet 1 Original Filed Aug. 2,1940 FIG.

I INVENTOR. JOHN A. fv/AUHE/i JR uff AGENT only: U a/100.31

Feb. 21, 1950 J. A. MAURER, JR

IMPULSE RECORDING OPTICAL SYSTEM Original Filed Aug. 2, 1940 2Sheets-Sheet 2 Q b ll ||Q 8l||ll|| ||||l.||6 Q II II!!! S 0E PatentedFeb. 21, 1950 IMPULSE RECORDING OPTICAL SYSTEM John A. Maurer, J r., NewYork, N. Y., assignor to J. A. Maurer, Inc., Long Island City, N. Y., acorporation of New York Application November 21, 1944, Serial No.564,453,

which is a division of application Serial No. 349,515, August 2, 1940,now Patent No. 2,437,470, dated March 9, 1948. Divided and thisapplication July 24, 1947, Serial No. 763,193

4 Claims. 1

This invention relates to optical systems for the photographic recordingof electrical impulses on a moving film such as are used in soundrecording, picture transmission, and the like, and this application is adivision of my application Serial No. 564,453, filed November 21, 1944,as a division of my application Serial No. 349,515, filed August 2,1940; applications Serial No. 349,515 and Serial No. 564,453 being alsoassigned to J. A. Maurer, Inc., a corporation of New York, applicationSerial No. 349,515 now being abandoned, and application Serial No.564,453 now being Patent No. 2,437,470, granted March 9, 1948.

More particularly, the invention relates to op-, tical systems of theclass referred to above wherein a small mirror vibrated by anoscillograph galvanometenbr "a similar'device for translating electricalimpulses into mechanical vibrations,

' modulates a light beam in accordance with the electrical impulses tobe recorded. The mirror oscillograph recording optical systems knownheretofore, however, have the disadvantage that the light flux from therecording light source, such as the filament of an incandescent lamp, isnot efficiently utilized therein. This unfavorable condition is due tothe fact that the aperture of the oscillograph mirror is the limitingaperture in the two co-ordinate planes of the known optical systems, andthat it cannot be enlarged beyond a certain degree since the physicalsize of the mirror must be comparatively small in order to avoiddistortions due to its mass. For a given light source, therefore, theamount of light flux reaching the moving film is unduly limited in thoseoptical systems, and this limitation makes itself particularly felt whenfilters are used at some position in the optical system, for example,for selecting light rays of a certain wave length, or for otherpurposes.

Another drawback of the known mirror oscillograph recording opticalsystems is that a portion of the light fiux from the recording lightsource is not effectively prevented therein from falling on parts otherthan the oscillograph mirror, or on the structure housing the opticalsystem. This portion of the light flux is to some extent reflecteddiffusely, thus forming stray light even though the surfaces on which itis incident may be black. Such stray light is objectionable because itmay cause an additional exposure of the moving film, which should beexposed only to light flux modulated by the oscillograph mirror.

It is, therefore, an object of the present invention to provide a mirroroscillograph recording 2 optical system which is highly eflicient asregards the utilization of the light flux from the recording lightsource.

Another object of the invention is the provision of such an opticalsystem whose limiting aperture can, in one of its co-ordinate planes, be

made much larger than the aperture of the oscillograph mirror.

Another object of the invention is the provision of such an opticalsystem wherein the formation of stray light isreduced to a negligibleamount.

Another object of the invention is the provision of such an opticalsystem which is particularly satisfactory as regards ease of manufactureand convenience of adjustment.

More specifically, however, it is an object of the invention to providea mirror oscillograph recording optical system which embodies thefeatures recited above, and which may be built at materially reducedcost.

A further object, of the invention is the provision of such an opticalsystem which may be built with small physical size and greatcompactness.

Still other objects of the invention include those which are hereinafterstated or apparent, or which are incidental to the invention;

In the optical system according to the invention, the oscillographmirror is adapted to vibrate M about a horizontal axis while the film'moves'past the recording point in a substantially vertical direction,the recording point being the point at which the optical axis of thesystem strikes the film. The optical system also has means for forming auniformly illuminated light spot whose horizontal extension varies in avertical direction. Further means are provided in the optical systemwhich effect an imagery of this light spot in such a manner that it isconjugate to the recording point in both the vertical and horizontalplanes of the optical system. Otherwise, however, the imagery of thelight spot is different in the two co-ordinate planes. In the verticalplane, the light spot is first imaged at a horizontal slit by imagingmeans acting in the vertical plane and then at the recording point byimaging means acting in only the vertical plane, the horizontal slitbeing placed between the oscillograph mirror and the recording point. Inthe horizontal plane, on the other hand, an intermediate image of thelight spot is formed substantially on the mirror by first imaging meanswhich act in only the horizontal plane. The intermediate image, in itsturn, is imaged at a position beyond the recording point by secondimaging means which act in only the horizontal plane, and reimaged atthe recording point by third imaging means which act in the horizontalplane. By virtue of this arrangement, the mirror is substantially at acommon focus-of two imaging means which act in only the plane containingits axis of vibration, and the limiting aperture in the horizontal planeis the apparent aperture-as seen from the recording point-of the secondimaging means. The apparent aperture of; the second imaging means,however, can easily be made at least ten times as large as the apertureof the oscillograph mirror.

The means for forming the light spot, furthermore, include a recordinglight source and a screen with an opening. The opening is uniformlyilluminated by light fiux from the light source, and its intermediateimage is formed substantially on the oscillograph mirror as has beenexplained hereinabove. At the same time, an image of the light source isformed substantially on the mirror by the action of a condenser lens inthe vertical plane. In this manner, substantially all the light fluxentering the optical system through the opening is controlled by theoscillograph mirror whereby the formation of stray light is reduced to anegligible amount.

The cost of building the optical system according to the invention,finally, may be materially reduced by substituting for the abovementioned first and second imaging means a single imaging means whichlikewise acts in only the horizontal plane. To that end, the light beamproceeding through the optical system is made to strike the oscillographmirror at an angle which is so small that the single imaging means canbe traversed by both the incident and reflected parts of the light beam.The single imaging means then forms the intermediate image of the lightspot substantially on the mirror and, simultaneously, images theintermediate image at the position beyond the recording point. The angleat which the light beam strikes the mirror, is made sufficiently smallpreferably by folding the incident part of the light beam whereby, atthe same time, a very compact mechanical structure is obtained for theoptical system.

In the foregoing brief explanation of the state of the art and summaryof the invention, and throughout the present specification, the termco-ordinate planes designates two planes at right angles to each otherwhose line of intersection is the optical axis of the system. Thehorizontal plane is the co-ordinate plane which contains the axis of theoscillograph mirror and the slit, while the vertical plane is theco-ordinate plane at right angles to the horizontal plane. The plane ofthe slit, finally, is the plane which contains the slit, and is at rightangles to both the vertical and horizontal planes.

In the present specification, the terms "vertical" and horizontal" thusare not used in any absolute sense but merely in order to distinguishbetween two planes, or directions, at right an les to one another, andchoice between these terms has been determined solely by convenience indescription and illustration.

The invention will be better understood when the following descriptionis considered with the accompanying drawings of certain presentlypreferred embodiments thereof, and its scope will be pointed out in theappended claims.

two cylindrical lenses shown in Figs. 1 to 3 have been replaced by asingle cylindrical lens, and

Fig. 6 is a perspective view of a modification of a part shown in Figs.1 to 3 and 5.

Referring first to Figs. 1 to 3, these figures show, by way of example,a variable area recording optical system which embodies the invention.The optical system has a light source such as the filament ill of anincandescent lamp i i. The light flux from lamp filament iii uniformlyilluminates a triangular opening it in a screen it so that a uniformlyilluminated triangular light spot is formed at screen it. The light beamdefined by lamp filament it and opening it; proceeds through the opticalsystem and is deflected by the mirror v[Il of an oscillographgalvanometer (not shown) or similar device for translating electricalimpulses into mechanical vibrations. It thus has a part which isincident from opening it upon mirror ll, and a part which is reflectedfrom' mirror ii towards the recording point 271. Recording point 27 isthe point at which the optical axis of the system strikes the film 23,and film 23 moves past recording point 27 in a substantially verticaldirection as indicated by the arrow More particularly, opening it is anisosceles triangle whose base extends horizontally, and mirror W isadapted to vibrate about an axis i@i8 which likewise extendshorizontally. Furthermore, a horizontal slit 2.! is formed in a screen22 which is placed between mirror ii and recording point El.

A spherical condenser lens i2 is placed between lamp ii and screen Ml,and a cylindrical lens l5 which has its cylinder axis vertical, isplaced between screen is and mirror ii. In front of mirror ii there isplaced a second spherical lens l9 which acts on the reflected as well asthe incident part or the light beam proceeding through the opticalsystem. A second cylindrical lens 32 which also has its cylinder axisvertical, is placed between mirror It and screen 22, while betweenscreen 22 and recording point 27 there is placed a third spherical lens43. Between spherical lens 43 and recording point 21, finally, there isplaced a third cylindrical lens M which has its cylinder axishorizontal.

These six imaging means have focal lengths relative to the other partsof the optical system as follows (see Figs. 2 and 3) Spherical lens l2has one of its conjugate foci at lamp filament l0, and the othersubstantially at mirror 91, that is, either on mirror I! or at aposition close thereto. Cylindrical lens i5 has one of its conjugatefoci at opening l3, and the other substantially at mirror I 1 so that anintermediate image of opening I3 is formed substantially on mirror Ill.Spherical lens I9 has one of its conjugate foci at opening 13, and theother at slit 2|. Cylindrical lens 42 has one of its conjugate foci atthe intermediate image of opening I3, and the other at a position Abeyond recording point 21. Spherical lens 43 has one of its conjugatefoci at position A, and the other at recording point 21. Cylindricallens 4 I, finally, has one of its conjugate foci at slit 2|, and theother at recording point 21.

'By virtue of the arrangement described here inabove of its variousparts, the following imagery is performed in the optical system of Figs.1 to 3:

In the vertical plane (Fig. 2), spherical lens I9 forms an image of theuniformly illuminated opening I3 in the plane of the horizontal slit 2|.This image of opening I3 moves vertically across slit 2| when mirror I1vibrates about the horizontal axis I8--I8. As much of slit 2| as isilluminated by the image of opening I3, is imaged at recording point 21by cylindrical lens 4 I. There thus is formed at recording point 21 ahorizontal line image of the illuminated portion of slit 2|, and thisline image has sharp and distinct hori zontal boundaries. Likewise inthe vertical plane, spherical lens I2 forms an image of lamp filamentII! substantially on mirror I1, thereby filling mirror I1 with light andalso aiding in the uniform illumination of opening I3 by lamp filamentIII.

In the horizontal plane (Fig. 3), cylindrical lens I5 formssubstantially on mirror I1 the intermediate image of opening I3, and animage of the intermediate image is formed by cylindrical lens 42 atposition A. The image at position A, in its turn, is imaged at recordingpoint 21 by spherical lens 43. By virtue of this successive imagery ofopening I3 in the horizontal plane, the horizontal line image atrecording point 21 has, in addition to its sharp and distinct horizontalboundaries, also sharply defined ends.

Lenses I2 and I9 are spherical and hence have power in the horizontal aswell as in the vertical plane. But their actions in the horizontal planecan be disregarded for the following reasons:

On account of its position and relative focal length, spherical lens I2tends to image lamp filament IIJ substantially on mirror I1 also in thehorizontal plane. The action, however, of cylindrical lens I5 interfereswith this imagery to such an extent that it becomes immaterial forattaining the objects of the present invention. On the other hand, thepower of spherical lens I9 in the horizontal plane has no effect uponthe action of cylindrical lenses I5 and 42 on account of the proximityof spherical lens I9 to mirror I1 which is, in the horizontal plane,substantially at a common focus of cylindrical lenses I5 and 42. Noactions, therefore, of spherical lenses I2 and I9 have been indicated inFig. 3.

Lens 43 is likewise spherical and hence has power in the vertical aswell as in the horizontal plane. But its action in the vertical plane isimmaterial because, in this plane, its power is small compared to thepower of cylindrical lens M. No action, therefore, of spherical lens 43has been indicated in Fig. 2.

Cylindrical lenses I5 and 42, in their turn, do not interfere with theimagery in the vertical plane since they have their cylinder axesvertical, and hence act in only the horizontal plane. Correspondingly,cylindrical lens 4| does not interfere with the imagery in thehorizontal plane since it has its cylinder axis horizontal, and henceacts in only the vertical plane,

The imagery performed in' the vertical and horizontal planes of theoptical system of Figs. 1 to 3 thus brings it about that recording point21 is conjugate to opening I3 in both co-ordinate planes. In thevertical plane, horizontal slit 2| is, with respect to spherical lensI9, conjugate to a horizontal line through opening I3, for example, thebroken line aa shown in Fig. 4. Since, furthermore, recording point 21is in the vertical plane conjugate to slit 2| with respect tocylindrical lens 4|, it is also conjugate to line aa. The line image atrecording point 21 hence is an image of line aa as far as its verticalextension, or width, is concerned, and it is, according to a well knownproperty of conjugates, made up of the light flux emanating from lineaa. Moreover, this light flux is brought to a focus at recording point21 also in the horizontal plane, namelyas has been explainedhereinab0veby the successive actions of cylindrical lenses I5 and 42 andof spherical lens 43. The line image at recording .point 21 hence is animage of line a-a also as far as its horizontal extension, or length, isconcerned. When, therefore, the horizontal line through opening I3 isshort-as is, for example, the broken line bb in Fig. 4the line image isalso short, while it is long when that horizontal line is longas is, forexample, the broken line c-c in Fig. 4.

The particular horizontal line through opening I3 to which recordingpoint 21 is conjugate, is determined by the angle of inclination ofmirror I1. Normally, mirror I1 is adjusted so that at its rest position,that is, when no electrical impulses are applied to the oscillographgalvanometer on which it is mounted, recording point 21 is conjugate toline aa, which line passes through opening I3 halfway between its tipand its base. When then the electrical impulses to be recorded areapplied in known manner to the oscillograph galvanometer, mirror I1vibrates in accordance therewith about the horizontal axis III-48, andin such a manner that, when the amplitude of its vibration is a maximum,recording point 21 is conjugate to line b--b at the one extreme of itsmotion and to the line 0-0 at the other extreme thereof. The length ofthe line image at recording point 21 hence varies in accordance with thevibration of mirror I1 and, therefore, the electrical impulses to berecorded. A variable area track 28 thus is produced on film 23 as itmoves past recording point 21.

As has been explained hereinabove, recording point 21 is conjugate toopening I3 or, more exactly, to a horizontal line through opening I3, inthe horizontal as well as the vertical plane of the optical system ofFigs. 1 to 3. The imagery, however, which results in-this condition, isdiiferent in the two co-ordinate planes. In the vertical plane. openingI3 is imaged at slit 2| by spherical lens I9 which acts in the verticalplane, and slit 2| is imaged at recording point 21 bv cylindrical lens4| which acts in only the vertical plane. Since spherical lens I9 isplaced in front of mirror I1 and images opening I3 immediately at slit 2I, the light flux from opening I3 is-ln the vertical planediffused atmirror I1. This is necessary because the vertical plane is the planethrough which the light beam is deflected when mirror I1 vibrates aboutthe horizontal axis I8--I8, thereby selecting. in cooperation with thehorizontal slit 2!, horizontal lines through opening I3 which becomeconjugate to recording point 21.

In the horizontal plane, on the other hand, an intermediate image ofopening I3 is formed substantially on mirror I1 by cylindrical lens I5.and this intermediate image is imaged at position A by cylindrical lens42 and re-imaged at recording point 21 by spherical lens 43 which actsin the horizontal plane. Since cylindrical lenses I6 and 42 act in onlythe horizontal plane, mirror II is substantially at a common focus oftwo imaging means which act in only the plane containing its axis ofvibration I8--I8. For any given angle of inclination of mirror I'I,therefore, the amount of light flux from opening I3 which is acted uponby cylindrical lens 42, is limited by the aperture of this lens ratherthan the aperture of mirror ll. Moreover, since the light flux actedupon by cylindrical lens 42 is brought to a focus at position A andthence focussed at recording point 21 by the action of spherical lens43, the limiting aperture in the horizontal plane is not the actualaperture of cylindrical lens 42, but its apparent aperture as seen fromrecording point 21. The apparent aperture of cylindrical lens 42,however, mayin view of the action of spherical lens 43--be made at leasttwice as large as its actual aperture which, in its turn, may be made asmuch as five times as large as the aperture which it is practical togive to mirror II. The limiting aperture in the horizontal plane of theoptical system of Figs. 1 to 3 hence can easily be made at least tentimes larger than the aperture of mirror II.

The result thus obtained by means of the novel imagery embodied, by wayof example, in the mirror oscillograph recording optical system of Figs.1 to 3 represents a marked advance over the prior art. In the knownoptical systems, the light flux from the entrance position correspondingto opening I3 is diffused at the oscillograph mirror in the twoco-ordinate planes so that the mirror aperture is the limiting apertureof the optical systems alsoin the co-ordinate plane which contains themirror axis. Since the physical size of the oscillograph mirror must becomparatively small in order to avoid distortions due to its mass, theabove condition has been a serious obstacle to an eillcient utilizationof the light flux in the prior art optical systems. The advantage gainedin this respect by the imagery according to the invention isconsiderable because, as is well known to those skilled in the art, theefiiciency with which the light flux from a given light source isutilized in an optical system, is approximately proportional to theproduct of the limiting apertures in the two co-ordinate planes of theoptical system.

Another advantage of having, in the optical system of Figs. 1 to 3,mirror I! substantially at a common focus of two imaging means which actin only the horizontal plane, is that small deviations of mirror I Iabout a vertical axis have a negligible effect on the imagery in thehorizontal plane. Mirror I I need therefore be accurately adjusted onlyabout the horizontal axis I8-I8. This greatly increases the ease ofadjustment of the optical system, and is particularly important when itis necessary to replace the oscillograph galvanometer on which mirror I1is mounted.

A further advantage of the imagery performed in the optical system ofFigs. 1 to 3 resides in the fact that there is formed substantially onmirror II an image of lamp filament II) by the action of spherical lensI2 in the vertical plane, and simultaneously the intermediate image ofopening I3 by the action of cylindrical lens I 5 in the horizontalplane. It thus is possible so to control the light flux entering theoptical system through opening I3 that it is all incident within theworking aperture of mirror II. This result is best obtained when thefocal length of spherical lens I2 and the position of lamp II are chosenso that the image of lamp filament II) has a vertical dimension nolarger than that of mirror I], and when the focal length of cylindricallens I5 and the position of screen I4 are chosen so that the largesthorizontal dimension of the intermediate image is no larger than thehorizontal dimension of mirror II. If these conditions are fulfilled,all the light flux passing through opening I3 is subject to control bymirror I'I, whereby the formation of stray light in the optical systemis reduced to a negligible amount.

The employment, finally, of cylindrical lens 4| in the portion of theoptical system between screen 22 and recording point 21 has certaininherent advantages: Cylindrical lens 4I may have a short focal lengthso that the optical system may be built with small physical size.Moreover, a cylindrical lens of short focal length is less expensivethan a spherical lens, or lens system, well enough corrected to form,over the same distance, an equally sharp line image. The optical systemof Figs. 1 to'3 may hence be built with greater compactness and at lesscost than the mirror oscillograph recording optical systems knownheretofore.

The cost of building an optical system according to the invention may befurther reduced by making the light beam defined by lamp filament In andopening I3 strike mirror II at a small angle. It then is possible tosubstitute a single.

cylindrical lens II for the two cylindrical lenses I5 and 42 of Figs. 1to 3. Like cylindrical lenses I5 and 42, cylindrical lens II has itscylinder axis vertical, and it is placed so as to be traversed by thereflected as well as the incident part of the light beam deflected bymirror I1. The relative focal length of cylindrical lens II is chosen.so that opening I3 and a position on, or close to, mirror II areconjugate with respect to cylindrical lens II on the incident part, andthis position and position A, or an equivalent position, are conjugatewith respect to cylindrical lens II on the reflected part of the lightbeam. In this manner, cylindrical lens II forms the intermediate imageof opening I3 substantially on mirror I! and, simultaneously, images theintermediate image at a. position other than the recording point 21.

One way of making the angle at which the light beam strikes mirror II,suificiently small consists in considerably lengthening the opticalsystem mechanically. But, while such an arrangement materially reducesthe cost of building the optical system on account of the replacement oftwo cylindrical lenses by a single cylindrical lens, it sacrifices thecompactness of its mechanical structure. The latter disadvantage isovercome in, and a very compact mechanical design of the optical systemis provided by, the arrangement shown in Fig. 5 by way of example. Inthis arrangement, a reflecting prism 10 is placed between screen I4 andmirror I1 whereby the incident part of the light beam is folded so thatit strikes mirror I! at a small angle, and cylindrical lens II istraversed by both the incident and reflected parts of the light beam. Inplace of prism "I0 there may be employed other suitable beam foldingmeans such as mirrors, or the like.

It has been pointed out hereinabove that, while spherical lens 43 haspower in both the vertical and horizontal planes, its action in thevertical plane is immaterial. Spherical lens 43 may thus be replaced inthe optical system of Fig. 5 as well as in that of Fig. 1 by acylindrical lens 44-, shown in Fig. 6, which has its cylinder axisvertical and hence acts in only the horizontal plane. Like sphericallens 43, cylindrical lens 44 is placed between screen 22 and recordingpoint 21 and has one of its conjugate foci at position A, and the otherat recording point 21. The effect of cylindrical lens 44 upon theimagery in the horizontal plane, therefore, is the same as that ofspherical lens 43.

It, furthermore, will be understood by those skilled in the art that theoptical system of Fig. 5 is susceptible also to most of the othermodifications shown and described in Patent No. 2,437,470 with respectto the optical system of Fig. 1. For variable area recording, thevarious openings, or pairs of openings, shown in Figs. 5 to 10a ofPatent No. 2,437,470 may be substituted for the opening in the screen i4also in the optical system of Fig. 5 so as to form at screen Hiinconjunction with lamp filament I and condenser lens l2-a uniformlyilluminated light spot whose horizontal extension varies in a verticaldirection, or a pair of such light spots.

.For variable'density recording, there may be employed in the screen l4a rectangular opening in conjunction with either a penumbra stop or alight shading member as shown in Figs. 11 and 12, respectively, ofPatent No. 2,437,470. The light spot formed at screen l4 then isofuniform horizontal extension and vertically varying illumination, butthe light fiux emanating from it is vertically graded as in the case ofthe aforementioned openings whose horizontal extension varies in avertical direction.

Moreover, also in the optical system of Fig. 5, spherical condenser lensl2 and spherical lens l9 may each be replaced by a cylindrical lenswhose cylinder axis is horizontal, and which has the same focal lengthrelative to the other parts of the optical system as the spherical lensit replaces; see Figs. 13 and 14 of Patent No. 2,437,470.

Finally, whenever the optical system of Fig. is employed for variablearea recording, cylindrical lens II should preferably be well correctedfor spherical and chromatic aberration, and for coma, for the reasonsset forth in Patent No. 2,437,470.

What is claimed is:

1. In an impulse recording optical system, the combination of light beamdefining means which include means for forming a light spot ofvertically graded light flux; arecording point past which a fihn maymove in a substantially vertical direction; .a mirror adapted to vibrateabout a horizontal axis, said light beam being deflected by said mirrorso as to have a part which is incident from said light spot upon saidmirror, and a part which is reflected from said mirror towards saidrecording point; means placed between said mirror and said recordingpoint, and forming a horizontal slit; a cylindrical lens placed betweensaid light spot and said mirror and between said mirror and said slitforming means, said cylindrical lens having its cylinder axis verticaland being traversed by said incident and reflected parts; first imagingmeans placed in front of said mirror, and acting in the vertical plane;second imaging means placed between said slit forming means and saidrecording point, and

acting in the horizontal plane; and third imaging means placed betweensaid second imaEiTi g' means and said recording point, and acting inonly the vertical plane: said light spot and said mirror being conjugatewith respect to said cylindrical lens on said incident part, said mirrorand a position beyond said recording point being conjugate with respectto said cylindrical lens on said reflected part, said light spot andsaid slit being conjugate with respect to said first imaging means, saidposition and said recording point being conjugate with respect to saidsecond imaging means, and said slit and said recording point beingconjugate with respect to said third imaging means.

2. In an impulse recording optical system, the combination ofllight beamdefining means which include means for forming a light spot ofvertically graded light flux; a recording point past which a film maymove in a substantially vertical direction; a mirror adapted to vibrateabout a horizontal axis, said light beam being deflected by said mirrorso as to have a part which is incident from said light spot upon saidmirror, and a part which is reflected from said mirror towards saidrecording point; means placed between said light spot and said mirrorfor folding said incident part; means placed between said mirror andsaid recording point, and forming a horizontal slit; a cylindrical lensplaced between said folding means and said mirror and between saidmirror and said slit forming means, said cylindrical lens having itscylinder axis vertical and being traversed by said incident andreflected parts; first imaging means placed in front of said mirror, andacting in the vertical plane; second imaging means placed between saidslit forming means and said recording point, and acting in thehorizontal plane; and third imaging means placed between said secondimaging means and said recording point, and acting in only the verticalplane: said light spot and said mirror being conjugate with respect tosaid cylindrical lens on said incident part, said mirror and a positionbeyond said recording point being conjugate with respect to saidcylindrical lens on said reflected part, said light spot and said slitbeing conjugate with respect to said first imaging means, said positionand said recording point being conjugate with respect to said secondimaging means, and said slit and said recording point being conjugatewith respect to said third imaging means.

3. The combination defined in claim 2, and wherein said second imagingmeans is a spherical lens.

4. The combination defined in claim 2, and wherein said second imagingmeans is a cylindrical lens having its cylinder axis vertical.

JOHN A. MAURER, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,157,166 Dimmick May 9, 19392,173,681 Dimmick Sept. 19, 1939 2,436,148 Maurer Feb. 17, 19482,437,470 Maurer Mar. 9, 1948

